Not yet...........it does sound very clean to the ear, but I will take some
distortion measurements a little further down the time line. Initial results
are encouraging................no distortion evident on fading signals.

Pete

starman wrote in message
...
Pete KE9OA wrote:

Just a follow up on the MW receiver design...............I have
completed
all of the RF stuff. The rest is up to the software folks at work.
MDS is .08uV, overload takes place at 50,000uV. The overload will be
better
on the final product..........I will use a VCA ahead of the 1st mixer.
I still may try to figure out a way to use the TDA1572's on board
oscillator........I don't know yet. Maybe tomorrow at work.
I have completed the quasi-synchronous detector, requiring only one
chip
(Philips SA637). Very similar sounding to the low distorion envelope
detector on the TDA1572, except for slightly better readability when
signals
are at the system noise floor (.08uV), and no distortion occuring when
there
is signal fading.
A couple of people have e-mailed me about this design, so I will
reiterate.
The quasi-synchronous detector consists of a mixer and a high gain
limiting
amplifier. The I.F. signal is split into two paths. One path is applied
to
the RF port of the mixer, while the other path is applied to the input
of
the high gain limiting amplifier.
The limiting amplifier amplitude variations from the I.F. signal,
providing
a square wave at the intermediate frequency. The output of the limiting
amplifier is fed to the LO port of the mixer, and the demodulated audio
is
taken from the I.F. output port of the mixer.

Pete

Have you measured the final audio output distortion w/wo the sync'
detector working, to get an idea of how well the sync' works during a
selective fade?


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